A toy example of a constraints solver, provided by Cognisys (https://cognisys.co.uk/). We are given four four-digit numbers, and told for each how many digits are a) in the right place, b) in the wrong place. For example:

1453 => “one digit is in the right place, and one is in the wrong place”

There are (implicitly) no repeat digits. Guess the combination.

You could do this iteratively, and solving by hand, we’d start with the strongest constraint first. But we’re programmers, and thinking is hard. Since there’s only 10,000 combinations, why not just test them all?

Cast your minds back - or possibly don’t, it wasn’t a fun time - to the Great Toilet Paper Shortage of 2020, early on in the pandemic. The supply of toilet paper was fine, but demand skyrocketed - and some enterprising folk decided to exacerbate this by buying in enormous bulk with the intention to resell. Almost everywhere, this was condemned as price gouging - which it was - and in many cases, the oppressed rolls of the people were liberated by law enforcement, no doubt to go to a better place.

Spend some time on Reddit - which you probably shouldn’t - or read the original Terry Pratchett - which you should - and you’ll probably come across the Sam Vimes “boots” theory of Socioeconomic Unfairness.

""" The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money.

Take boots, for example. He earned thirty-eight dollars a month plus allowances. A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. Those were the kind of boots Vimes always bought, and wore until the soles were so thin that he could tell where he was in Ankh-Morpork on a foggy night by the feel of the cobbles.